Research data supporting "Probing Oxide-Ion Mobility in the Mixed Ionic-Electronic Conductor La$_2$NiO$_{4+δ}$ by Solid-State $^{17}$O MAS NMR Spectroscopy"

17O solid-state MAS variable-temperature NMR spectra of La2NiO4+δ at 4.7 T, 7.05 T, and 16.4 T, at variable temperature between 35°C and 140°C; pseudo-2D T1 saturation recovery data. Additional 17O solid-state MAS NMR spectra of a mixture of mixture of La2NiO4+δ, La3Ni2O7 and La4Ni3O10 at 7.05 T at room temperature; and of La2O3 at 16.4 T at variable temperature between 35°C and 135°C. Raw XRD data as plotted in Figure S1 and S13 (SI). Raw TGA data as plotted in Figure S2 (SI). Calculations of NMR parameters as output from the solid-state density functional theory (DFT) code CRYSTAL09, using the geometry-optimised structure files. All experimental and computational parameters are given in the article and/or data files.